What Turing Did After He Invented the Universal Turing Machine Author(S): B
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What Turing Did after He Invented the Universal Turing Machine Author(s): B. Jack Copeland and Diane Proudfoot Source: Journal of Logic, Language, and Information, Vol. 9, No. 4, Special Issue on Alan Turing and Artificial Intelligence (Oct., 2000), pp. 491-509 Published by: Springer Stable URL: http://www.jstor.org/stable/40180239 Accessed: 04/11/2009 17:35 Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available at http://www.jstor.org/page/info/about/policies/terms.jsp. JSTOR's Terms and Conditions of Use provides, in part, that unless you have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and you may use content in the JSTOR archive only for your personal, non-commercial use. Please contact the publisher regarding any further use of this work. Publisher contact information may be obtained at http://www.jstor.org/action/showPublisher?publisherCode=springer. 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JACKCOPELAND and DIANE PROUDFOOT The TuringProject, University of Canterbury,Private Bag 4800, Christchurch,New Zealand E-mail: bjcopeland@canterbury. ac. nz, [email protected]. ac. nz; http://www.AlanTuring, net (Received 1 June 1999; in final form 15 April 2000) Abstract Alan Turing anticipated many areas of currentresearch in computer and cognitive science. This article outlines his contributions to Artificial Intelligence, connectionism, hypercomputation, and Artificial Life, and also describes Turing's pioneering role in the development of electronic stored-programdigital computers. It locates the origins of Artificial Intelligence in postwar Britain. It examines the intellectual connections between the work of Turing and of Wittgenstein in respect of their views on cognition, on machine intelligence, and on the relation between provability and truth. We criticise widespread and influential misunderstandings of the Church-Turing thesis and of the halting theorem. We also explore the idea of hypercomputation, outlining a number of notional machines that "compute the uncomputable." Key words: Artificial Intelligence, Artificial Life, Automatic Computing Engine (ACE), Church- Turing thesis, Colossus, connectionism, Halting theorem, history of computing, hypercomputation, Turing, Wittgenstein 1. The Race to Build the First Computer It is often said that, apart from specifying the universal Turing machine in 1935, Turingplayed little or no role in the development of computers. The reality is very different. In 1945 Turing produced a detailed design for his proposed Automatic Computing Engine or ACE (Turing, 1945; Copeland, 1999a; Copeland, 2000b). This design was the first relatively complete specification of an electronic stored- program general-purpose digital computer. The slightly earlier "First Draft of a Report on the EDVAC,"produced by the Moore School group at the University of Pennsylvania (Von Neumann, 1945), contained little engineering detail, in partic- ular concerning electronic hardware.Turing, on the other hand, supplied detailed circuitdesigns and specifications of hardwareunits, specimen programsin machine code, and even an estimate of the cost of building the machine (£1 1,200). Turing saw that speed and memory were the keys to computing. His design had much in common with today's RISC architecturesand called for a high-speed memory of roughly the same capacity as an early Macintosh computer (enormous by the standardsof his day). Had Turing'sACE been built as planned it would have 492 B.J.COPELAND AND D. PROUDFOOT been in a different league from the other early computers, but his colleagues at the National Physical Laboratory(NPL) thought the engineering work too difficult to attempt, and a considerably smaller machine was built. Known as the Pilot Model ACE, this machine ran its first program on May 10, 1950. With a clock speed of 1 MHz it was for some time the fastest computer in the world. Sales of DEUCE, the production version of the Pilot Model ACE, exceeded 30 (confounding a prediction by a top adviser to the NPL that Britain's computing needs would be satisfied by a total of 3 digital computers). The fundamentals of Turing's ACE design were employed by Harry Huskey (at Wayne University, Detroit) in the Bendix G15 computer. The G15 was arguably the first personal computer and over 400 were sold worldwide. DEUCE and the G15 remained in use until about 1970. Another computer derived from Turing's ACE design, the MOSAIC, played a role in Britain's air defences during the Cold Warperiod; other derivatives include the Packard-BellPB250 (1961). Unfortunately,delays beyond Turing's control resulted in the NPL's losing the race to build the world's first electronic stored-programdigital computer- an hon- our that went to the University of Manchester, where, in the Royal Society Com- puting Machine Laboratory,the "Manchester Baby" ran its first program on 21 June 1948. As its name implies, the Baby was a very small computer,and the news that it had run what was only a tiny program - just 17 instructions long - for a mathematically trivial task was "greeted with hilarity" by the team building the sophisticated Pilot Model ACE.* Turingdesigned the programmingsystem for the Ferranti Mark I, the production version of the Baby's successor.**Completed in 1951, the Ferranti Mark I was the first commercially available electronic digital computer;about 10 were sold (in Britain, Canada, Holland and Italy). Both the ACE and the Manchester computer came out of research that nobody would have guessed might have a practical application. In a lecture in Cambridge in 1935 the mathematicianMax Newman - whose own role in the development of computers has been insufficiently emphasised - introduced Turing to the concept that led directly to the Turing machine: Newman defined a constructive process as one that a machine can carry out (Copeland, 1999b).* Turingtook Newman's words literally and the result was a typescript, which Turing showed to Newman in April 1936, setting out the concept of the universalTuring machine.** According to New- man, Turingwas interestedright from the startin the possibility of actually making * Michael Woodger (Turing's assistant at the NPL from May 1946) in personal communication with Copeland (1998). ** ' A digital facsimile of Turing's typewritten Programmers Handbookfor Manchester Electronic Computer is in the Turing Archive for the History of Computing and may be viewed on-screen at http://www.AlanTuring.net * Newman in interview with Christopher Evans in 1976 ("The Pioneers of Computing: an Oral History of Computing," Science Museum: London). ** The Turing machine concept was announced by Turing in an address to the London Math- ematical Society on 12 November 1936, "On Computable Numbers, with an Application to the Entscheidungsproblem" (Turing, 1936). TURINGAFTER THE UTM 493 a machine of the sort described in the paper.*In 1937-1938 Turing designed and wired up a simple binary multiplier,but it was not until the development during the war of high-speed electronic switching that the dream of building a miraculously fast general-purposecomputing machine really took hold. Following decades of secrecy, Turing's wartime work as leading codebreaker at the GovernmentCode and Cypher School, Bletchley Park, is now well known. F.H. Hinsley, official historian of British Intelligence in the Second World War, has estimated that the Bletchley Park codebreakers shortened the war in Europe by as much as two years. Turing's main work concerned the 'Enigma' code (his "Treatiseon the Enigma" has recently been declassified). Newman, in a different section, attackedthe 'Fish' codes. Based on binary teleprintercode, Fish was used in preference to Morse-based Enigma for the encryption of high-level signals, for example messages from Hitler and other members of the German High Command. Newman realised that the attack on Fish could be mechanised (Turing had already mechanised the attackon Enigma, with enormous success) and at Turing's sugges- tion sought the help of electronic engineer Tom Flowers.**The history of electronic data-processingbegins with Flowers' pre-warwork at the Post Office Research Sta- tion at Dollis Hill in London: during the period 1934-1939 Flowers experimented with high-speed electronic data-storageand designed electronic digital telephone equipmentthat used 3,000-4,000 vacuum tubes runningcontinuously. Flowers has remarkedthat at the outbreakof war with Germanyhe was possibly the only person in Britain who realized that vacuum tubes could be reliably used on a large scale for high-speed digital computation. During 1943, in consultation with Newman, Flowers designed and built Colossus, the first large-scale